The present invention relates to a nuclear reactor plant with a light water reactor, comprising a containment having an upper space and a lower space, which is separated from the upper space by a separating member and which is arranged to house a cooling medium, and a reactor vessel housing a reactor core and provided in the upper space.
Such nuclear reactor plants are known and these have proved to function in a satisfactory manner. However, if the reactor core for any reason would reach such a temperature that the fuel starts to melt and the geometry of the core is changed, it might happen that the core may fall down from its original position and penetrate the bottom of the reactor vessel, i.e., a so-called core melt. In this case, the core will fall down onto the bottom surface of the containment. As long as the containment is intact and the core may be maintained within the containment, there is no real risk that radioactivity in any greater amount will leak to the environment. However, if the core would melt through the containment, the risk for such a leakage is imminent.
Different measures have been-proposed in order to avoid this risk. One such measure is to sprinkle cooling liquid over the core located on the bottom surface. However, such a cooling from above may prove to be insufficient, during a longer period of time, to prevent in a secure manner any part of the core from penetrating the containment. Another measure proposed is to let the core fall down into a water pool provided beneath the reactor vessel. A further measure, which has been proposed, is to let the core fall down into a container having double walls between which a cooling medium circulates to cool down the core.